Where can I buy diclofenac patches in the US at a good price?
These should be off-topic. They don't have much to do with health. Also these could be opinionated and too broad because the USA is a big place, so there is no right answer.
The way this is handled on Fitness is that if it is being used in an ongoing fitness program, it can be on topic. It's the difference between:
"What's a good bench for a home gym?"
"I have Bench X, and when I do decline presses, I lose stability in my shoulders. Is there a better bench that will support me when I do declines?"
Still a shopping recommendation, but it addresses a specific facet, and the use of the item. The first invites speculation and lots of "Well I like X" type answers.
So, if the poster can address how they are using it to maintain/enhance health and what they are looking for specifically, it can be on topic.
Shopping topics would be off topic since the laws of what can be bought in the health care market will vary from place to place and for somethings it can even be against the law if you don't make the purchase in the correct place.